Magnetic levitation is a form of transportation in which a vehicle is moved via magnetic levitation without contacting the ground. As such, the vehicle is able to move without experiencing rolling friction with the ground or support rails, for example. In general, the vehicle travels along a guideway via magnets that generate lift and propulsion, thereby reducing friction and allowing travel at high speeds.
Currently, magnetic levitation systems are being developed in which a vehicle travels through vacuum tubes, in order to reduce the effects of aerodynamic drag on the vehicle. As such, the speed and operational efficiency of the vehicle are increased through the elimination or reduction of aerodynamic drag with respect to the vehicle. The magnetic levitation system reduces static and rolling friction with respect to the vehicle, while the vacuum tube reduces aerodynamic drag. A reduced friction vehicle system, such as a magnetic levitation vehicle that travels through a vacuum tube, may be positioned underneath a ground surface, and/or may be supported over the ground surface.
The tube may vertically deflect as the vehicle travels therethrough. The deflections of the tube under vertical load applied by the vehicle traveling therein may be unsettling to passengers. For example, a magnetic levitation vehicle system may include vacuum tubes constructed of steel. For a tube of a given diameter sized such that one atmosphere (atm) of pressure creates a stress equal to an allowable stress divided by a safety factor, for example, the deflections for a tube with supports spaced 300 feet apart is approximately 0.095 inches. Such a magnitude of deflection may cause discomfort to passengers aboard the vehicle traveling through the tube.
In order to reduce tube deflections, a tube of increased strength and robustness may be used so that the bending moment of inertia is increased. If the diameters of the tubes are held constant, the amount of weight is inversely proportional to the deflections. Thus, in order to achieve reduced deflections to 0.045 inches, for example, the tube would need to be twice the weight. As can be appreciated, tubes of increased size and weight increase the overall cost of the transportation system.
As another option, the spacing between support columns that support the tube above the ground may be reduced. Notably, tube deflections are proportional to the fourth power of the spacing between support columns. As an example, by moving support columns closer by sixteen percent (to 252 feet instead of 300 feet), deflections may be reduced to 0.045 inches. Again, however, reducing the spacing between support columns requires an increased number of support columns, which increases the overall cost of the transportation system.
Alternatively, the support columns may be eliminated by locating the tubes below the ground surface through tunneling. However, the process of tunneling substantially increases the cost of the transportation system. Overall, tunnels are more expensive than above ground systems. Additionally, pressures exerted into the tubes that are below ground are typically greater than one atmosphere, which is the pressure exerted upon an above ground tube. As such, the increased pressure may require stronger (and expensive) tubes to be used.